1. Field of the Invention
The present invention relates to an adaptive antenna for use with a base station for a mobile communication system, a local area radio communication system, and so forth.
2. Description of the Related Art
As an antenna for use with a base station for a mobile communication system, an antenna that form a plurality of sector beams is used. In the antenna, an area of 360 degrees on a horizontal plane of the base station is covered with a plurality of beams. As an example, six beams with a beam width of 60 degrees are disposed in the circumferential direction. As an antenna that forms sector beams, a dipole antenna with reflector is known. In this antenna, the beam width depends on the size of the reflector and the height of the dipole to the reflector.
However, such an antenna that form a plurality of beams does not have a means for controlling the difference of communication amounts of beams in the service area that the base station covers. For example, in an area of a particular sector beam, the communication amount is very large. In an area of another sector beam, the communication amount is very small. Such a situation often takes place. When the communication amounts are unbalanced among beams on the time base, such a problem can be solved by initially changing the beam widths of sector beams or initially changing the number of channels that are accommodated in the individual sectors. But in the case that unbalanced communication traffic may often change, it is difficult to overcome such a problem by using the conventional antenna.